Abstract
This paper explores the potential of the Series Active Variable Geometry Suspension (SAVGS) for comfort and road holding enhancement. The SAVGS concept introduces significant nonlinearities associated with the rotation of the mechanical link that connects the chassis to the spring-damper unit. Although conventional linearization procedures implemented in multi-body software packages can deal with this configuration, they produce linear models of reduced applicability. To overcome this limitation, an alternative linearization approach based on energy conservation principles is proposed and successfully applied to one corner of the car, thus enabling the use of linear robust control techniques. An H∞ controller is synthesized for this simplified quarter-car linear model and tuned based on the singular value decomposition of the system's transfer matrix. The proposed control is thoroughly tested with one-corner and full-vehicle nonlinear multi-body models. In the SAVGS setup, the actuator appears in series with the passive spring-damper and therefore it would typically be categorized as a low bandwidth or slow active suspension. However, results presented in this paper for an SAVGS-retrofitted Grand Tourer show that this technology has the potential to also improve the high frequency suspension functions such as comfort and road holding.
Highlights
According to MarketsandMarkets, the automotive suspension market will be worth $ 66.2bn by 2018, and most of the premium/luxury vehicles will be equipped with active or semi-active suspensions
Omission of lateral tire forces In most suspension studies that focus on comfort and road holding, the vehicle is assumed to be moving in a straight line and at a constant forward speed over an uneven road
The results shown confirmed the intuitive idea that a nominal angle close to θS(Lne) ≈ θS(Lmin) + ΔθS(Lne), with ΔθS(Lne) = 90 deg, provides the best attitude control performance (θS(Lmin) represents the passive equilibrium configuration, as shown in Fig. 1-a, and θS(Lmin) + 90 deg a situation in which the single mechanical link (SL) is almost perpendicular to the SD)
Summary
According to MarketsandMarkets, the automotive suspension market will be worth $ 66.2bn by 2018, and most of the premium/luxury vehicles will be equipped with active or semi-active suspensions. The work significantly advances previous work (Cheng et al, 2015) and provides a number of new contributions, including: 1) an energy-based methodology for the derivation of simple linear quarter-car models of series active suspensions with lumped geometric nonlinearity, that are accurate for a wide range of operating conditions (Section 2), as opposed to linearized models that are only accurate about a single trim condition; 2) the synthesis of an /∞ controller for the SAVGS, effectively tuned for comfort and road holding enhancement by looking at the singular values and singular directions of the system (Section 3), rather than tuned exclusively by iteration based on control bandwidth and simulation results; 3) the introduction of exogenous disturbances into the /∞ synthesis framework, beyond road disturbances, to control motions related to load transfer arising from longitudinal and/or lateral vehicle accelerations, and to provide suspension deflection tracking capability at low frequencies for future integration of low and high frequency suspension controls (Section 3); 4) the introduction into the /∞ synthesis framework of additional measurement signals based on the expected availability of sensors, and of an account of the dynamics of the actuator and its (inner) position control loops (Section 3); and 5) the assessment of the SAVGS performance and of the quality of the proposed control, in comparison to passive suspension, when the vehicle is subjected to a wide range of standard disturbances by virtually testing its operation through simulation with nonlinear, multi-body, quarter-car and full-car models (Section 4).
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